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Many moons ago the fixing options available to developers bolting routes were limited yet this was a time of morphing away from the genesis of pure trad’ to some fixed gear and later full blown sport routes.

Typically caving bolts were the only fixing available for climbers to use however we climb in different times now and so developers should and can use plenty of rated (EN959 / UIAA 123) fixings.

There is value in climbers learning to recognise rated hardware just as they would not use traditional equipment not rated for rock anchor purposes.

The inherent issue with sport climbing is the total reliance on assumed fixings that will hold in the event of falls.

For a number of years, decades even, the choice of material for fixed rock anchors (bolts) was pretty much limited to stainless steel grades 304 or 316.

With the development of climbing areas within highly corrosive environments, so to has been the development in both anchor technology and climber knowledge concerning corrosion and its various mechanisms as they apply to rock climbing anchors.

Stress Corrosion Cracking (SCC) and the alarming rapidity with which anchors are rendered dangerous has gripped the community on a global scale and driven the development of titanium resin bonded anchors as a direct result. The investigation of SCC in Southern Thailand has had an impact within the materials engineering world by raising awareness that SCC can occur outside of the conditions traditionally believed to be the required norms.

Climbers equipping new routes have the choice of an excellent range of stainless steel products for normal use and equally titanium where SCC / harsh corrosion is affecting hardware. With Fixe introducing their PLX range and Petzl with an ‘HCR’ product line, what are the benefits and are those products anything better?

Fixe PLX

The Fixe PLX range is based on duplex stainless steel grade 2304, although may contain a blend of other duplex stainless steels.

Duplex stainless steels have good resistance to SCC however remain affected by pitting and crevice corrosion, both types of corrosion that can act as initiator mechanisms whereby SCC develops at a later stage.

926 grade stainless steel should contain a minimum of 6% Molybdenum and generically is described as a high corrosion resistant steel.

UIAA studies underway intend to determine a range of materials as matched to a set of environmental conditions since simply stating something is corrosion resistant is meaningless without equally specifying the corrosion it is supposed to resist. The use of the term HCR is misleading in that regard.

Duplex steel has high resistance to SCC and high quality steels in the 6% Molybdenum range resist SCC so where does that leave climbers trying to ascertain the relevance of these new products against what already exists on the market? Two considerations foremost in mind is the cost of the fixing and known performance in real world climbing applications. Looking at pricing online with no discounts applied:

316 grade stainless steel is a cost effective option in areas not affected by SCC.

Fixe’s PLX hardware is roughly around the same price band of Titan Climbing’s titanium hardware but the Petzl ‘HCR’ is quoted at an astronomical US$ 36 (pack of 20 list price).

Performance

316 and Titanium already has proven use in a variety of regions with varying degrees of corrosion. Where SCC is occurring, a titanium bolt glued in with pure epoxy is currently considered the best form of fixed protection.

Fixe have just initiated a batch recall for their PLX bolts in response to severe corrosion affecting hangers. The reasons for this are not currently in the public domain but this does highlight the issue facing developers when new products are launched to either build in company liability where the product line was only 316 based or perhaps to counter titanium based products. Without a ‘track record’ developers take the risk in installing hardware only to find it won’t last some 5, 10 years or longer, later.

Technical materials knowledge within the oil and gas industry says 6% Moly’ steels will resists SCC however the UIAA is yet to issue a guideline to climbers to this effect. The fundamental issue facing the use of Petzl’s ‘HCR’ range however is cost and it is simply too expensive unless the unit price is reduced to become competitive with titanium glue-ins. The drawbacks associated with using bolt ins however are not eliminated.

Ultimately when the track record of certified titanium glue-in bolts is considered, the advantages this type of fixing offers, and the pricing for a known SCC resistant material, why switch to duplex 2304.

The seminar covered a range of topics covering risk, bolt types, standards, corrosion and the materials from which certified bolts are manufactured. Key objectives of the seminar were to assist climbers in recognising suspect bolts and the need to be aware of whether bolts have failed before climbing in unfamiliar climbing areas.

This well attended event also provided the opportunity to discuss Stress Corrosion Cracking (SCC) via a question and answer session.

The current practice of both the UIAA 123 and EN 959 standards has been to leave anchor corrosion/SCC resistance as the responsibility of the manufacturers. However, numerous incidents of fixed rock climbing anchors failures mostly in seaside locations show that this approach is not optimal.

The Safety Commission of Union Internationale des Associations d’Alpinisme (UIAA) is preparing a new standard, which will classify anchors into classes according to their resistance to SCC and / or corrosion. The UIAA SafeCom working group consists of technical experts supported by regional volunteers around the globe who are providing failed bolt samples and also installing test cells of different bolts which are being monitored over time for corrosion behaviour.

Hong Kong is located within a region that has an elevated corrosivity potential and failed samples recovered during re-bolting work / catastrophic failures have been provided to the working group in recent years.

All samples of failed / corroded hardware were sent to the University of Chemical Technology in Prague where Tomas Prosek and his team conducted visual analyses at cross-sections using metallographic techniques and by scanning electron microscopy (SEM). Material chemical composition was verified by x-ray fluorescence (XRF) analyser, chemical composition of deposits and corrosion products determined by energy dispersive spectroscopy (EDX).

Samples submitted included hangers, bolts and the cracked anchor set from Green Slab in Sea Gully.

Crevice corrosion occurred on all four analysed hangers, either under a washer or between a hanger and rock. There were branched cracks on two analysed hangers, one of them was completely torn after failure under 5 kN force (Hour Glass Crack). Cracking was observed also on both sleeves in a longitudinal direction of the bolts. Cross-section and SEM analysis after removal of corrosion products showed branched transgranular crack morphology.

The Green Slab anchor set featured a crack located 1–2 mm from the weld on the chain-link attached to one of the hangers that showed intergranular morphology, which suggests sensitization of heat affected zone during welding leading to intergranular corrosion or intergranular SCC.

The conclusion from the preliminary report confirms that chloride presence was principal for the classical low-temperature chloride-induced SCC to occur and it is probable that concentration of chlorides in confined zones (e.g. behind hangers, washers and nuts) helped to initiate the SCC, at least in some cases. Crevice corrosion in this case occurs where salt solution (sea water) remains stagnant behind hangers.

Hong Kong geology can be very broadly defined as either volcanic tuff, or coarse grained granite, and neither rock type features magnesium in the concentrations required to form aggressive magnesium chloride based solutions that are found in limestone climbing areas like Tonsai. Super accelerated SCC is unlikely to be a problem for Hong Kong sport crags however the change in anchor type from multi component expansion bolt to a single piece glue-in bolt or adopting certified titanium glue-in bolts on sea side sport cliffs will reduce the rate of corrosion or in the case of titanium; eliminate it altogether.

Acknowledgement and thanks is extended to Alan Jarvis of the UIAA and Tomas Prosek and his team in Prague.